1. Field of the Invention
The present invention relates to an arrangement for activating a deployment mechanism of a restraint system for vehicle occupants; specifically the deployment mechanism is connected to a secondary side of a transfer unit.
2. Background Invention
A restraint system is described in German Patent No. DE 24 33 555 A1. The restraint system described is an airbag arranged in a steering wheel. In order to bypass the complex and failure-prone slip rings or volute springs previously used to transfer signals between a control unit located on the vehicle chassis and the deployment mechanism (firing pellet) installed in the airbag, according to this existing art a rotary transfer unit is used, whose primary and secondary windings are arranged rotatably with respect to one another about the steering wheel axis. The firing pellet of the airbag is connected to the secondary winding, and the primary winding is connected via a switch to a battery of the vehicle. By means of pulses fed in on the primary side, a voltage which leads to deployment of the firing pellet is induced in the secondary winding. In order for the voltage induced in the secondary winding to be great enough to deploy the firing pellet, the magnetic coupling between the primary and secondary windings of the transfer unit must be very high. A high magnetic coupling is achieved by embedding both windings in ferromagnetic coil elements. A transfer unit of this kind is capable of receiving a great deal of energy, even if its winding terminals erroneously come into contact with the vehicle's voltage lines. In some circumstances, however, this energy is already sufficient to deploy the airbag. Improper deployment of this kind should, however, be prevented in all cases.
In German Patent No. DE 44 04 816 A1, an arrangement for activating a deployment mechanism of a restraint system is described in which the supply voltage for the deployment mechanism is transferred directly from the primary side to the secondary side of a transformer. A voltage regulator prepares the voltage transferred to the secondary side for the deployment mechanism and for other electronic circuits on the secondary side. As a result, a relatively high supply voltage must continuously be transferred via the transformer, which in turn requires a high magnetic coupling--associated with the aforementioned disadvantages--between the primary and secondary windings of the transformer.